pgsql: Fix NULL input behaviour of pg_stat_get_replication_slot().

Fix NULL input behaviour of pg_stat_get_replication_slot().

pg_stat_get_replication_slot() accidentally was marked as non-strict, crashing
when called with NULL input. As it's already released, introduce an explicit
NULL check in 14, fix the catalog in HEAD.

Bumps catversion in HEAD.

Discussion: https://postgr.es/m/20220326212432.s5n2maw6kugnpyxw@alap3.anarazel.de
Backpatch: 14-, where replication slot stats were introduced

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/43a7dc96eb363f87286494223861301361ce766c

Modified Files
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src/include/catalog/catversion.h | 2 +-
src/include/catalog/pg_proc.dat | 2 +-
src/test/regress/expected/stats.out | 7 +++++++
src/test/regress/sql/stats.sql | 4 ++++
4 files changed, 13 insertions(+), 2 deletions(-)